The present invention relates to a method for calibrating a distance sensor of a rotary actuator device for controlling a charge cycle valve of an internal combustion engine. In particular, this method is applied here to rotary actuator devices without mechanical end stops.
In traditional internal combustion engines, the camshaft for controlling the charge cycle valves (also known as gas exchange valves) is driven mechanically by the crankshaft via a control chain or a control belt. To increase engine power and reduce fuel consumption, considerable advantages are achieved by controlling the valves of the individual cylinders individually. This is possible for a so-called fully variable valve drive (variable control times and variable valve lift), e.g., a so-called electromagnetic valve drive. With a fully variable valve drive, an “actuator unit” is allocated to each valve and/or each “valve group.” At the present time, different basic types of actuator units are being researched.
With one basic type (so-called lift actuators) an opening magnet and a closing magnet are allocated to a valve or a valve group. By applying electric power to the magnets, the valves can be displaced axially, i.e., opened and/or closed.
With the other basic type (so-called rotary actuator) a camshaft is provided with cams whereby the control shaft is pivotable back and forth by an electric motor.
To regulate a rotary actuator, extremely accurate sensor values are required, providing information about the instantaneous position of the rotary drive element and/or the element driving the drive element of the rotary actuator itself, e.g., the position of the actuator element driven by the rotor (e.g., the camshaft) or the rotor position itself In known rotary actuator devices, distance sensors are calibrated by the approach to mechanical stops, which define the end positions of a control cam.
German Patent Document DE 101 40 461 A1 describes a rotary actuator device for control of the lift of a charge cycle valve with such mechanical stops. The lift control of the charge cycle valves is accomplished here by an electric motor which is itself controlled by characteristics maps and which has a shaft with a control cam connected to it in a rotationally fixed manner arranged on the rotor of the electric motor. During operation of the internal combustion engine, the rotor of the electric motor swings, i.e., oscillates back and forth, and the control cam periodically forces the charge cycle valve into its open position by means of a pivot lever. The charge cycle valve is closed by the spring force of a valve spring. In order for the electric motor not to have to overcome the entire spring force of the valve spring when opening the charge cycle valve, an additional spring is mounted on the shaft. The forces of the valve spring and additional springs are such that in periodic operation of the rotary actuator device, the kinetic energy is either stored in the valve spring (closing spring) or in the additional spring (opening spring) in accordance with the position of the charge cycle valve. The invention is directed to unambiguously positioning the control cam by a first rotary stop and a second rotary stop, thereby unambiguous positioning of the control cam in its end positions. However, one disadvantage of this arrangement is that the calibration of distance sensors for determining the position by approach to mechanical stops does not have a satisfactory precision for all applications. Depending on the design of the rotary actuator device used, the mechanical tolerances of the systems are so great that the required accuracy cannot be achieved.
An object of this invention is to provide a method for measuring and calibrating a distance sensor for a rotary actuator device by which more accurate positioning, and/or determination of the position of the actuator element (and thus also the gas exchange value) is ensured. In particular, a method is to be provided which reliably ensures a measurement and/or calibration in operating phases when the rotational speed of the internal combustion engine is low as well as in operating when the rotational speed of the internal combustion engine is high.
According to this invention, this object is achieved by at least one state variable of the electric motor being determined and compared with a stored reference quantity. In the event of a deviation between the state variable so determined and the reference quantity with which it is to be compared beyond a predetermined value, the stored setpoint path on the basis of which the electric motor and/or the rotor of the electric motor is regulated and/or the value determined by the distance sensor is altered as a function of the size of the deviation of the state variable from the reference value.
The state variable is preferably determined by measuring the corresponding value. As an alternative, however, the state variable may also be calculated on the basis of a stored model. The rotor angle, a time derivation of the rotor angle and/or the electric power of the electric motor or a quantity proportional to the motor current (motor power, supply voltage of the electric motor) is preferably determined as the state variable of the rotor angle.
The change in the stored setpoint path and/or the distance sensor value measured preferably takes place by multiplying the stored setpoint path values and/or distance sensor values times a correction factor and/or by adding a stored offset value. The correction factor and/or offset value are referred to below as the correction value. The correction value is determined as a function of the distance deviation measured. This determination may be performed by selection from a stored table or by online calculation. In the case of a high distance deviation (above a predetermined first deviation threshold) on the basis of which the rotor threatens to drop to an unwanted intermediate position, for example, a correspondingly high correction value is assigned so that directly in the same work cycle or in the immediately following work cycle of the rotor, this value is regulated on the basis of strongly corrected values. A drop in the rotor into the intermediate position described here is thus effectively prevented. In the case of a smaller path deviation, the existence of which does not mean a drop in the rotor is imminent, the at least one monitored state value which is determined in each working cycle or in every n-th working cycle may be averaged over a number of working cycles. An assignment and/or determination of a corresponding correction factor is/are then performed in particular on the basis of the averaged correction factor. A working cycle in the sense of the present invention is a term referring to the opening or closing process of a charge cycle valve in particular and/or the respective swiveling operation of the rotor of the electric motor immediately thereafter. A definition of the working play that includes the closing process and the opening process is also possible.
Since no gas backpressures need be taken into account during the closing process, the inventive method is preferably used in calibration of the distance sensor during the closing process of the charge cycle valve assigned to the distance sensor.
The method according to this invention includes in particular two different strategies for measuring, i.e., calibrating the rotary actuator. The first strategy consists of determining minor deviations in the rotor from the predetermined setpoint path on the basis of which it is regulated to detect, to average them over a plurality of working cycles and, depending on the averaged deviation, to make a change in the setpoint path on the basis of which the rotor is then regulated in the future and/or to alter the distance sensor signals such that a distance characteristic corrected accordingly will be regulated in the future on the basis of the modified distance sensor signals. This strategy thus extends in time over several working cycles (slow intervention). In contrast with that, the second strategy consists of counteracting major deviations with a rapid regulating intervention. This is done by the fact that the regulation of the rotor is already performed in the same working cycle or in the next working cycle on the basis of the altered values for the setpoint path and/or the distance sensor signals by means of a corresponding change in the setpoint path and/or the distance sensor signals. The two strategies also differ, however, in the measures to be taken, which will be discussed after the following description of the figures.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.